The present invention relates to the air conditioning of an internal space.
The air conditioning of an internal space such as a living room, factory, garden house, fermentation room, drying room, cold storage, etc. is carried out for adjusting air temperature, humidity, flow, and clarity to a condition suitable for the purpose and uniformly distributing them throughout the internal space. The adjustment of these four factors of the air to a condition suitable for the purpose at hand can already be substantially achieved thanks to the development of air conditioning apparatuses such as heating and cooling apparatuses, drying and humidifying apparatuses, air cleaning apparatuses, etc. However, uniform distribution of the four air factors throughout an internal space cannot yet be fully achieved because of insufficient development of technologies for making the conditions of the internal space uniform and for air exchange. Therefore, a number of unsolved problems remain in the air conditioning of factories, garden houses, cold storages, etc.
An object of the present invention is to provide a method for ventilating an internal space to achieve uniform distribution of temperature, humidity, flow, and clarity of the internal air and air exchange between the internal air and external air.
According to the present invention, there is provided a method for ventilating an internal space by rotating air flow comprising a step of blowing out a jet of internal air having a vertically long rectangular cross section and uniform blowout velocity distribution over the cross section horizontally along the side wall of the internal space to generate a horizontal rotating air flow over the whole internal space, thereby inducing a horizontally circulating air flow and a vertically circulating air flow over the whole internal space.
The present ventilating method by rotating air flow is based on the theory of xe2x80x9cRotating Flow on a Planexe2x80x9d (Greenspan, H. P:The Theory of Rotating Fluids, Cambridge Univ. Press, 1968) published in 1968 by H. P. Greenspan, who established the theory based on the analysis of the airflow of tropical storms.
The theory of xe2x80x9cRotating Flow on a Planexe2x80x9d will be explained based on FIG. 1. In the horizontally rotating air flow of a tropical storm, a pressure field directed toward the center of the rotation is generated because of the generation of vacuum pressure accompanying the rotation of the air. Centrifugal force generated by the rotation of the air and the radial force directed toward the center of the rotation generated by the pressure field are in balance.
Close to the ground surface, the centrifugal force decreases because the viscosity of the air decreases the circumferential velocity of the air flow. Close to the ground surface therefore, a radial air flow directed toward the center of the rotation is induced by the pressure field directed toward the center of the rotation. The radial air flow changes directions at a point close to the center of the rotating air flow to form a secondary flow directed vertically upward.
The present ventilating method by rotating air flow effectively achieves uniform distribution of air temperature, humidity, flow, clarity in the internal space by utilizing a horizontally rotating air flow over the whole internal space and the vertically upward secondary air flow induced by the horizontally rotating air flow.
In the present ventilating method by rotating air flow, a jet of internal air having a vertically long rectangular cross section and uniform blowout velocity distribution over the cross section is blown out horizontally along the side wall of the internal space. Energy loss of the jet of internal air having a uniform blowout velocity distribution over the cross section and low blowout velocity caused by the entrainment of ambient air is small. Therefore, the jet of internal air circulates in the internal space along the side wall of the space with its vertically long rectangular cross section maintained. The horizontally rotating flow of the jet of internal air is transmitted to the air of the central portion of the internal space and the air of the upper and the lower portion of the internal space through friction force to induce a horizontally rotating air flow over the whole internal space. Close to the floor surface, a radial air flow directed toward the center of the internal space is induced by the imbalance between the centrifugal force and the force directed toward the center of the internal space due to the pressure field.
The radial air flow forms a secondary flow directed vertically upward at the center of the internal space. The vertically rising secondary flow reaches the center of the ceiling of the internal space to flow radially toward the side walls of the internal space. The secondary flow reaching the upper end of the side walls flows down along the side walls. Thus, a horizontally circulating flow and a vertically circulating flow of internal air are induced over the whole internal space. The horizontally circulating flow and the vertically circulating flow agitate the internal air to make the distribution of temperature, humidity, flow and clarity of the internal air uniform.
According to the present invention, there is provided a method for ventilating an internal space by rotating air flow comprising a step of blowing out a jet of internal air having a vertically long rectangular cross section and uniform blowout velocity distribution over the cross section horizontally along the side wall of the internal space to generate a horizontal rotating air flow over the whole internal space, thereby inducing a horizontally circulating air flow and a vertically circulating air flow over the whole internal space, and air exchange between the internal air and external air.
When ventilation windows in the side wall and the ceiling of the internal space are opened, external air entrained by the internal horizontally circulating air flow enters the internal space through the ventilation windows in the side wall. The external air horizontally circulates in the internal space and gradually joins the vertically circulating flow of internal air so that the combined flow leaves the internal space through the ventilation windows in the ceiling of the internal space. Thus, air exchange between the internal air and external air is induced. The horizontally circulating flow and the vertically circulating flow agitate the internal air to make the distribution of temperature, humidity, flow, and clarity of the internal air uniform.
According to a preferred embodiment of the present invention, the jet of internal air is blown out through a blowout elbow provided with guide vanes, wherein one or more guide vanes made of a curved plate and straight plates connected to the curved plate are disposed to make the shapes of the sub-channels defined thereby similar to each other based on the following formulas:
xe2x80x83po=h/{[f/(fxe2x88x92r)]mxe2x88x921}xe2x80x83xe2x80x83{circle around (1)}
an=por[f/(fxe2x88x92r)]nxe2x80x83xe2x80x83{circle around (2)}
bn=an/fxe2x80x83xe2x80x83{circle around (3)}
po: overhang length at the outlet of the elbow
h: inlet breadth of the elbow
f: enlargement ratio of the elbow (f=W/h)
W: outlet breadth of the elbow
m: number of sub-channels (mxe2x89xa72)
an: outlet breadth of n-th sub-channel (ao indicates the radius of curvature of the inner side wall and am indicates the radius of curvature of the outer side wall)
r: aspect ratio of the sub-channels
bn: inlet breadth of n-th sub-channel
The above mentioned blowout elbow is the one taught by Japanese Patent No. 2706222, U.S. Pat. No. 5531484, Chinese Patent No. 95102932.0 and Korean Patent No. 174734 belonging to the applicant of the present invention. A jet of internal air can be blown out through the above mentioned blowout elbow connected to an air blower.
Correlation between travel distance and air jet velocity in static air was measured for three kinds of air blowers: an air blower xe2x80x98axe2x80x99 consisting solely of an axial fan of 400 mm diameter, an air blower xe2x80x98bxe2x80x99 composed of the air blower xe2x80x98axe2x80x99 equipped with a rectification grid, and an air blower xe2x80x98cxe2x80x99 composed of the air blower xe2x80x98bxe2x80x99 equipped with a blowout elbow provided with guide vanes in accordance with Japanese Patent No. 2706222, U.S. Pat. No. 5531484, Chinese Patent No. 95102932.0 and Korean Patent No. 174734. Results of the measurements are shown in FIG. 2.
The initial velocity of the air jet by the air blowers xe2x80x98axe2x80x99 and xe2x80x98bxe2x80x99 was 11 m/s and the initial velocity of the air jet by the air blower xe2x80x98cxe2x80x99 with the enlargement ratio of 3.5 was 11 m/3.5≈3.1 m/s.
As seen from FIG. 2, the rates of velocity reduction of the air jets by the air blowers xe2x80x98axe2x80x99 and xe2x80x98bxe2x80x99 were large because the initial velocities of the air jets by the air blowers xe2x80x98axe2x80x99 and xe2x80x98bxe2x80x99 were large and the energy losses caused by air entrainment were large. The rate of velocity reduction of the air jet by the air blower xe2x80x98axe2x80x99 was especially large because the air jet by the air blower xe2x80x98axe2x80x99 had a swirling component that promoted entrainment of ambient air. The rate of velocity reduction of the air jet by the air blower xe2x80x98cxe2x80x99 was small because the air jet by the air blower xe2x80x98cxe2x80x99 was slow and rectified, so that the energy loss caused by the entrainment of ambient air was small.
Considering the fact that the mean velocity of the air flow in gardening houses is 0.25 m/s, the travel distances of the air jets before their velocities fell to 0.25 m/s were measured. As seen from FIG. 2, the travel distances of the air jets from the air blowers xe2x80x98axe2x80x99, xe2x80x98bxe2x80x99 and xe2x80x98cxe2x80x99 were 25 m. The sectional area of the outlet of the air blower xe2x80x98cxe2x80x99 was 3.5 times as large as those of the air blowers xe2x80x98axe2x80x99 and xe2x80x98bxe2x80x99. When considering the effective sectional area of the air jet with a velocity of 0.25 m/s at a travel distance of 25 m, the effective sectional area of the air jet from the air blower xe2x80x98cxe2x80x99 with small entrainment of ambient air is thought to have been far more than 3.5 times as large as those of the air jets from the air blowers xe2x80x98axe2x80x99 and xe2x80x98bxe2x80x99 with large entrainment of ambient air.
It is thought that the driving force inducing the horizontally circulating air flow in the internal space is proportional to the effective sectional area of the air jet at the travel distance. Therefore, the air blower xe2x80x98cxe2x80x99 is thought to be an effective means for embodying the ventilating method by rotating air flow. As described in the preferred embodiments, the effectiveness of the air blower xe2x80x98cxe2x80x99 was confirmed by field tests.